Large shipping containers have been fairly standardized in the maritime freight shipping industry. They are typically handled in large ports by loading and unloading derricks. Such derricks usually include an automated clamp or connector for attaching and disconnecting the huge crates. However, small ports using only cranes and small derricks do not have such facilities. They typically include a cable hoist having a central hoist hook with choker cables. The ends of the chokers often include shackles that can be connected only at the top corners of the containers. This process takes approximately twenty minutes for each container since the dock worker must climb to each top corner of the container and manually connect a shackle. The same process must be repeated for removing the shackles and chokers.
This problem has been realized to a limited degree by provision of "quick disconnect" lifting lugs for the shipping containers.
U.S. Pat. No. 4,139,228 to Thomas Varadi discloses a locking device for connection to shipping container lift fittings. The device includes a manual lock pin arrangement that can be fitted through the typical slot at the lift fitting and turned to a locked position. The pin is connected to a handle device that can be locked upon turning to an appropriate position through a spring-biased pin arrangement. This device includes several moving parts and requires several steps to lock it into place. The time consumed in placing and removing the device is substantial. Furthermore, the chance for error in positioning the device increases with the number of steps that must be performed by the dock worker in attaching and detaching the assemblies from the containers.
A somewhat similar lift coupling is disclosed in U.S. Pat. No. 4,068,878 to Irving Wilner. This patent discloses a rotatable locking lug that fits within the appropriate slots of a shipping container for connection to choker hooks. The device includes two relatively movable locking members that can be turned relative to one another and fitted in a cruciform configuration to lock the device into position. The device is preferably used along the top horizontal surfaces of the shipping container to avoid bending the central pivot shaft. If the device were to be used on the vertical sides or bottom corners of the container, lifting forces could quite easily bend the shank and inhibit or prevent pivotal motion of the locking members. The result could be the inability to remove the "jammed" lugs from the containers. It is important that no projections extend from the shipping containers as packing of the containers in tight quarters is necessary and such projections would damage adjacent containers.
It therefore has remained desirable to obtain some form of lifting lug arrangement for standard shipping containers that will enable quick and safe attachment and detachment of choker cables to shipping containers and that will remain reliable for use over an extended period of time.